21664719 has 16 divisors (see below), whose sum is σ = 32204640. Its totient is φ = 14394240.

The previous prime is 21664717. The next prime is 21664729. The reversal of 21664719 is 91746612.

21664719 is a `hidden beast` number, since 2 + 1 + 6 + 647 + 1 + 9 = 666.

It is not a de Polignac number, because 21664719 - 2¹ = 21664717 is a prime.

It is a super-2 number, since 2×21664719² = 938720098697922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664717) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7909 + ... + 10289.

It is an arithmetic number, because the mean of its divisors is an integer number (2012790).

Almost surely, 2^21664719 is an apocalyptic number.

21664719 is a deficient number, since it is larger than the sum of its proper divisors (10539921).

21664719 is a wasteful number, since it uses less digits than its factorization.

21664719 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2727 (or 2721 counting only the distinct ones).

The product of its digits is 18144, while the sum is 36.

The square root of 21664719 is about 4654.5374635940. The cubic root of 21664719 is about 278.7731998896.

The spelling of 21664719 in words is "twenty-one million, six hundred sixty-four thousand, seven hundred nineteen".